App Quiz Source

**Sources**
2016: http://time.com/4592864/most-popular-iphone-apps-2016/
2015: http://mashable.com/2015/12/09/apple-best-ios-apps-2015/#45LaFG0w7EqW
2014: http://www.ign.com/articles/2014/12/09/apple-reveals-2014s-most-downloaded-apps-movies-and-more
2013: http://gizmodo.com/the-app-stores-most-popular-apps-of-2013-1485021796
2012: http://www.adweek.com/digital/apple-lists-top-apps-of-2012/